Carbon nanotube catalysts: an approach toward nanodimensional reactions

Rochester Institute of Technology

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2003

Carbon nanotube catalysts: an approach toward

nanodimensional reactions

Mindy Gordon

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Carbon Nanotube Catalysts: An Approach Toward Nanodimensional Reactions

Mindy Gordon

July 2003

A thesis submitted in partial fulfillment of the requirements for the degree of

Master of Science in Chemistry

Approved:

Santhanam K.S.V.

Thesis Advisor

Terence C. Morrill

Department Head

Department of Chemistry

Rochester Institute of Technology

Copyright Release Form

Carbon Nanotube Catalysts: An Approach Toward Nanodimensional Reactions

I, Mindy Gordon, hereby grant permission to the Wallace Memorial Library, of

RIT, to reproduce my thesis in whole or in part.

Any use will not be for commercial use

or profit

.

Signature

Mindy Gordon

Table

of

Contents

Abstract

i

Acknowledgments

iii

Publications

iv

List

of

Figures

v

List

of

Schemes

vii

List

of

Tables

viii

List

of

Equations

viii

1.

Introduction

1

1

.

1

Structural Aspects

of

Carbon

1

1. 1. 1 Graphite

(amorphous)

1

1.1.2 Diamond

2

1. 1. 3 Carbon Nanotubes

2

1. 1.4 Synthesis of

Carbon

Nanotubes

3

1. 1.5

Structural

Representations

6

1

.2

Electrical

Properties

9

1

.3

Mechanical Properties

9

1

.4

Purification

and

Functionalization

of

Carbon Nanotubes

10

1.4. 1 Chemical Properties

12

1.4.2 Applications

13

1.5 Nanoscience

15

1.5.1 Nanodimensional

Reactions

16

2.

Experimental

19

2.1

Chemicals

19

2.2 Instrumentation

19

2.2.1

UV-VIS Analysis

of

the

Reaction

19

2.2.2

GC/MS

Characterization

of

the

Products

19

2.2.3

FT1R of

Carbon

Nanotubes

and

Products

20

2.2.4

TGA of

Carbon

Nanotubes

20

2. 2. 5

Fluorescence Spectra

ofAzobenzene

and

Products

21

2.2.6

Atomic Absorption of Carbon Nanotubes

21

2.2.

7

pH

of

the

Carbon Nanotubes

21

2.3 Procedures

21

2. 3. 1

Functionalization of Carbon Nanotubes

21

2.4

Oxidation

of

Aniline

22

2.5

Oxidation

ofp-Toluidine

22

2.6

Oxidation

of

Methylamine

23

2.7

Oxidation

of

Diphenylamine

23

3. Results

and

Discussion

23

3.1

Characterization

of

Carbon Nanotubes

23

3. 1. 1 Fourier Transform

Spectroscopy

Studies

23

3. 1.2 Thermogravimetric

Studies

25

3. 1. 3

Scanning

Electron

Microscopic Results

26

3.

1. 4 Transmission

Electron Microscopic Studies

27

3.3

Atomic Absorption

ofFunctionalized Carbon Nanotubes

29

3.4

Oxidation

of

Primary

Amines

30

3. 4. 1

Aniline-Discovery

of

the

Effect of

Carbon

Nanotubes

30

3. 4. 2

Influence of

Hydrogen

Peroxide Concentration

31

3.4.3

Role

of

Solvent

on

Oxidation

32

3. 4. 4

Test For Hydrogen Peroxide Inside

the

Nanotube

34

3.4.5

Possible Mechanisms

34

3.4.6

Catalysis

of

Carbon

Nanotubes

37

3.4.6.1

Estimation

of

Azobenzene Concentration

38

3.4.6.2

Azobenzene Diffusion Profiles

40

3.4.6.3

Suggestive Evidence For Reaction Inside

the

Nanotubes

42

3

.4.6.4

Stereospecificity

of

Azobenzene

43

3.4.6.5

Oxidation

under

Inert

atmosphere

43

3.4.6.6 Formation

of

NASH Product

44

3.5

Analytical Applications

46

3.6 Experiments

with

RPI Carbon Nanotubes

50

3.7

Effect

of

Silica

and

Light

52

3.8 Degradation

of

Carbon Nanotubes

52

3.9

Oxidation

ofp-Toluidine

53

3.9. 1

Spectral

and

Kinetic

Features

57

3.10

Oxidation

of

Methylamine

67

4. 1

Principle

67

4.

1. 1

Proposed

Construction

68

4.2

Preliminary

attempts and

Results

69

4.

2. 1

Simulation

of

the

Nanosynthetic Machine

69

4.2.2

Aniline

Oxidation

Reaction

71

4.2.2.1

Concentration

Dependence

of

Aniline

90

4.

2. 3

p-Toluidine

Oxidative

Reaction

90

4.2.4

Methylamine Reaction

101

4.2.5

Oxidation ofDiphenylamine

101

4.3

Relevance

of

Nanosynthetic Machine Concept in

Relation

to the

Existing Technology

103

5.

Conclusions

1 04

Abstract

The

oxidations of aromatic and aliphatic amines

have

been

investigated

to evaluate

the

catalytic effect of

functionalized

multiwalled carbon nanotubes.

Aniline

oxidation

by

hydrogen

peroxide produces

very low

yields of

azoxybenzene; similarly,

p-toluidine

oxidation produces azoxytoluene after

long

time periods.

When

functionalized

multiwalled carbon nanotubes are present

in

these

reactions,

the above oxidations produced unique products

such as azobenzene or azotoluene within a short period.

The

course ofthe reaction

has been followed

by

GC/MS

that showed a

mass number of

198

corresponding

to

azoxybenzene

(without

carbon

nanotubes)

or

182 corresponding

to azobenzene

(with

the

nanotubes).

The

first

stage of the oxidation

is identified

as

nitrosobenzene

formation

which

subsequently

couples with the

parent molecule to produce the azo compound.

UV-VIS

absorption

spectroscopy

showed no peak

in

the

absence of

the

carbon

nanotubes;

in

contrastto a

distinct

peak at

347

nmwhen

the

reaction

is

catalyzed

by

carbon nanotubes.

The

GC/MS data for

the/7-toluidine oxidation showed a mass spectral peak at a mass

number of

226,

corresponding

to

azoxytoluene,

which

is

replaced

by

210,

corresponding

to

azotoluene,

when

the

reaction

is

the

UV-VIS

absorption

data

showed an azotoluene peak at

464

nm.

To

reduce the unwanted product contribution

coming

from

the

outer

solution,

a carbon nanotube column was configured.

In

this

situation

100%

azobenzene

formation

was obtained when aniline

was oxidized.

The

efficiencies ofthe

different

columnsrange

from

50-97%

for

the

p-toluidine oxidation reaction.

The

oxidations of

diphenylamine

and methylamine

have

also

been

carried out

in

the

column configuration to understand the mechanisms.

The

results

suggest

the

feasibility

of

constructing

a nanosynthetic machine

for

Acknowledgments

My

advisor,

Dr. KSV

Santhanam,

for his

ideas,

patienceand

direction

My

committee:

Dr. T.C.

Morrill,

Dr.

G.

Takacs

and

Dr. M. Miri

for

theirguidance

and encouragement

Tom Allston

for

always

being

around

to

help

The RIT

Chemistry

Department for providing

the

funding

for

theresearch

Dr. P. Ajayan

at

RPI

for

carbonnanotubes and

allowing

us

to

usethe

SEM

and

TEM

Dr. D.D.L.

Chung

atthe

University

of

Buffalo

for

the

honeycomb

graphite

My family

and

friends for

all oftheir support-

1

_couldn't

have

made

it

without

any

of

Publications

(Refereed

Journals)

M.

Croston,

J.

Langston,

R.

Sangoi,

and

K.S.V.

Santhanam,

"Catalytic Oxidation

of

p-Toluidine

at

Multiwalled

Functionalized Carbon

Nanotubes",

J. Internal

Nanoscience,

1(3-4),

277-84

(2002)

-

A

special

issue

oncarbon nanotubes.

M.

Croston,

J.

Langston,

G.

Takacs,

T.

Morrill,

M.

Miri,

K.S.V. Santhanam

and

P.

Ajayan,

"Conversion

of

Aniline

to

Azobenzene

at

Functionalized Carbon Nanotubes: A

Possible

Case

of a

Nanodimensional

Reaction",

J. Internal

Nanoscience, 1(3-4),

285-94

(2002)

-

A

special

issue

on carbon nanotubes.

Posters/Presentations

M.

Croston,

J.

Langston,

G.A.

Takacs,

T.C.

Morrill,

M.

Miri,

and

K.S.V.

Santhanam,

Oxidation ofAniline

Catalyzed

by

Multiwalled

Carbon

Nanotubes,

poster,

ACS meeting

-

Rochester

division,

October 2001

M.

Croston,

J.

Langston,

R.

Sangoi,

and

K.S.V.

Santhanam,

Catalytic Oxidation

ofp-Toluidine

by

Multiwalled Carbon

Nanotubes,

presentation,

201st

ECS

meeting,

Philadelphia, PA

May

2002

M.

Croston

and

K.S.V.

Santhanam,

Concept ofNanosynthetic Machine

with

Functionalized

Carbon

Nanotubes,

poster,

ACS meeting

-

Rochester

List

of

Figures

Figure

1.

MWCNT

carbon arc

setup

3

Figure 2.

Apparatus for

thepreparation of

MWCNT

by

pyrolysis

4

Figure 3. Laser

ablation apparatus

for

the

preparationof

SWNTs

5

Figure 4.

Single-walled

carbon nanotube

6

Figure 5. Multi-walled

carbon nanotube

7

Figure 6.

Helicity

of a carbon nanotubes

7

Figure 7.

Helicity

of carbon nanotubes

8

Figure 8. Apparatus for

the thermal

annealing

of

CNTs

11

Figure 9. Irradiation

apparatus

for

purifying

nanotubes

12

Figure 10. Carbon

nanotubetransistor

from IBM

14

Figure 11. Reaction

inside

a carbon nanotube

16

Figure 12. FTJR

analysis ofcarbonnanotubes priorto

functionalization

24

Figure 13. FTIR

analysis ofcarbonnanotubes

following

functionalization

24

Figure 14. TGA

graph of

CNT

priorto

functionalization

25

Figure 15. TGA

spectrum of

CNT

after

functionalization

26

Figure 16. MWCNT

carbon arc method

setup

27

Figure 17. TEM

analysisofclosed carbon nanotube

28

Figure 18. TEM

analysis of a

functionalized

carbon nanotube

28

Figure 19. Photograph

of reaction

in

cuvettes

31

Figure 20.

1:1 Aniline:hydrogen

peroxide

in

acetone reactions

33

Figure 21. Azobenzene

in

acetonitrile reference spectrum

37

Beer's

Law

plot

for

cis-_{andtrans-azobenzene}

39

Figure

24.

trans-

Azobenzene

_{concentrationvs.}

time

for

varying

amounts of

CNT

40

Figure 25.

Simulation

of

Fick's

Law

error

function

curve

for

the

diffusion

of reactants

into

the

nanotubes and products out of

the

nanotubes

41

Figure 26. Extraction

ofthe solution

inside

the

nanotubes

42

Figure 27.

1M

aniline and

1M

hydrogen

peroxide

in

acetonitrile monitored

every

five

minutes

for

one

hour

-convection method

46

Figure 28. Breakdown

of

CNTs

in

hydrogen

peroxide

53

Figure 29. Simulation

ofp-toluidine reaction

54

.Figure

30.

/?-Toluidinewith

hydrogen

peroxide controlsolution

(0-50min)

58

Figure 31. Time-dependent

absorbance ofp-toluidinereaction with

CNT

59

Figure 32.

Linearity

of

the

growthof p,p'-dimethylazobenzenewithtime

60

Figure 33. Comparison

of

GC/MS

results of

1

:

1

p-toluidine

reactionwith

hydrogen

peroxide

61

Figure 34.

p'p-Dimethylazobenzene reference spectra

62

Figure 35. Kinetic study

of

1

:

1

/?-toluidine

to

hydrogen

peroxidereaction

66

Figure

36. Proposed

construction of nanosynthetic machine

68

Figure 37. Product

of aniline reaction

from

simulated

nanomachine

-first

collection

72

Figure 38.

GC

spectrum of nanotube column collection

80

Figure

39. Mass

spectrum of

the

first

collection

from

the

nanotube column

81

Figure 41.

UV-VIS

analysis of nanomachine product

83

Figure

42.

Analysis

of

O2

saturation of acetonitrile

88

Figure 43.

Analysis

of

N2

saturation of acetonitrile

89

Figure 44.

UV-VIS

spectra ofp-toluidinecollection vs. control

for

1

M

:

1 M

solution

94

Figure 45. UV-VIS

spectra of/?-toluidine collection vs. control

for

2M: 1M

solution

95

Figure 46.

p-Toluidine concentration

dependence

on azotoluenepeak

96

Figure 47.

%Conversion

ofp-toluidine

296nm

peak

99

Figure 48.

Azotoluene

formation in

nanomachine

99

Figure 49.

Nanomachine

collection

from diphenylamine

reaction

102

List

of

Schemes

Scheme 1.

Outline

of reaction mechanism

for

thecontrol solution.

35

Scheme 2.

Side-product formed

whenaniline andperoxide react

in

acetone.

35

Scheme 3.

Outline

ofthe carbon nanotubereaction

36

Scheme 4. Reaction

mechanism

forp-toluidine

in hydrogen

peroxide

control solution

56

Scheme 5. Side-product

of/?-toluidine

reacting in

acetone

56

Scheme 6. Mechanism

of/?-toluidine reaction

in

the

presence of

FMWCNT

57

Tables

Table

1.

pH of

Functionalized

Carbon Nanotubes

29

Table 2. Aniline Detection

Limits

47

Table 3.

GC/MS

Data

of

the

Catalysis

of

CNTs

48

Table 4.

GC/MS

Data

from Aniline

Reaction

49

Table 5. Comparison

of

RPI

and

DEAL Nanotubes

51

Table 6. Comparison

of

Kinetic

vs.

Convection Method for

/j-Toluidine

Reaction

63

Table 7. Measurements

for

Carbon Nanotube Columns

70

Table 8.

Specifications

for Aniline Reaction

73

Table 9.

GC/MS Analysis 22h

after

Collecting

from

Nanomachine

75

Table 10.

Specifications for

/?-Toluidine

Reaction

90

Table 11. GC/MS Analysis

ofp-Toluidine

Collections

92

Table 12. Concentration

of

Azotoluene

in Samples

with

Varying

Concentrations

of^-Toluidine

97

Table 13. Concentration

of

Azotoluene from 0. 1M

/?-Toluidine

Samples

98

Table 14.

Efficiency

of

CNT Column

100

List

of

Equations

Eq. 1 Beer's law

equation

39

Eq. 2 Fick's Law

of

Diffusion

41

1.

Introduction

The

synthesis of

fullerenes

and carbon nanotubes

may

be

considered as one of

the

important discoveries

ofthe 20th

Century.

Kroto,

Curl

and

Smalley (1)

pioneered the

effort when

they

began studying

a new allotrope ofcarbon called

the

fullerene.

Another

turning

point

in

the

history

of

the

chemistry

of carbon came with the

discovery

of

the

tubular structure of carbon

by

Iijima

[2],

which

is

rapidly

being

investigated

for

material

structure,

strength and catalytic properties.

This

thesis

is devoted

to theunprecedented

study

of catalytic properties of carbon nanotubes sin organic oxidative reactions which

may

be

amenable

for

the

construction of nanosynthetic machines

for

organic

preparations.

1.1

Structural Aspects

of

Carbon

There

are

four different

types

of graphite structures that will

be discussed:

diamond,

planar

graphite,

buckminsterfullerenes

and carbon nanotubes.

Diamond

exists

as a

face-centered

cubic unit cell

consisting solely

of carbon atoms.

Planar

graphite

consists of planes of carbon atoms arranged

in

hexagons

which

layer

each other.

Graphite

seems to

be

"slippery"

because

the planes can

be easily

separated

from

and

moved across each other.

This

is

why

graphite

is

used

in

pencils.

The

buckminsterfullerene

is

spherically

shaped with

the

carbon ends

forming

a pentagon to

close

the

sphere.

Nanotubes

are

formed in

somewhat

the

same

fashion,

either single or

multiple graphitic planes are rolled

into

a

tube

with carbon pentagons

existing

as

the

end

1.1.1

Graphite

(amorphous)

Graphite

bonding

is

sp2

hybridized

and exists as a

flat

plane and

has

a

3-fold

coordination system

[3].

1.1.2

Diamond

Whereas

graphite

is

sp2

hybridized,

diamond

existsas

sp3

hybridized

carbon

in

a

four-fold

coordinated structure

[3].

The C-C

bond distance

for diamond

is

larger

than

thatof graphite

due

to theweaker

forces

between

the

atoms

[3].

1.1.3

Carbon

Nanotubes

Multiwalled

carbon nanotubes

have diameters

from 10-50

nm and can

be 10

urn

in length

or

longer.

Multiwalled

nanotubes

have

a

density

of

1-2

g/cm3

and a

very large

surface areaof

10-20

m2/g.

Single

walled nanotubes

have

diameters

of

l-1.4nm

and can

be

as

long

as

100

urn.

Whereas

multiwalled nanotube

bundles

are

straight,

singlewalled

nanotube

bundles

are curled and

looped.

Carbon

nanotubes can exist

in

three

different

orientationsthat affect their electrical properties:

zigzag,

armchair and

chiral,

or

helical

[4].

Zigzag

nanotubes can either act as semiconductors or

metals,

armchair tubes are

mainly

semiconductors and chiral

tubes

are

primarily

metallic.

One

of

the

most

promising

characteristics of carbon

nanotubes,

other than

that

they

can

be

conducting

is

that

they

can

be ballistic

conductors,

which means

that there

will

be

no

scattering

of

electrons

[5].

They

also

have

the

highest

current

density

of

any

known

material at 108

A/cm [6].

Carbon

nanotubes are

approximately

100

times

stronger than steel with a

strength of

60,000

psi.

They

are also

very

light

with a

density

of

1.33-1.4

g/m3

Nanotubes

can

be

very

elastic

having

a

Young's Modulus

of

1500

GPa

[7].

They

also

have

a

high

thermal

conductance,

which

has been

measured at -2000

W/mK

at room

temperature

[8]

and,

they

have

electrical conductance properties comparable

to that

of

copper

(5.9x1

07

Qm)

[9].

When

nanotubes are

made,

they

form bundles

ofthemselves

that

contain all

three

orientations ofthenanotubes.

Researchers

at

IBM

have developed

a

method of

separating

the

metallic

CNT

from

the

semiconducting

CNT for

use

in

single

carbonnanotube

transistors

[10].

1.1.4

Synthesis of

Carbon

Nanotubes

There

are now

many

different

ways

in

which carbon nanotubes can

be

synthesized.

The

single walled tubesare

generally

made

by

laser

ablation of a graphite

rod

using

anickel or palladium metal catalyst.

MWCNTs

are

generally

prepared

by

the

carbon arc method

in

the presence of

helium

or

hydrogen

gas.

In

this

case,

no metal

catalyst

is

needed.

A. Anode B: Caihooe C:Collarette I): Deposit I 11eh-like\ul F.Soul (': DCpower

supph H Walcr-cooled

[image:18.484.94.389.416.630.2]

doublewall reav'Un

The

carbon arc method

for

producing

nanotubes

is

shown

in

Figure 1 [11].

The

cathode

and

the

anodeare

housed in

a

double-walled

water-cooled condenser.

When

a

20-25

V

DC

arc current

is

passed across

the

anode to the cathode

in

the

presence of

30-500 Torr

of

H2

or

He2

gas,

at

2500-3000

C,

the

cathode

length

begins

to

decrease

and

CNT

are

formed

[11].

Soot

is

collected

down

atthe

bottom

of

the

vessel.

The

cathode

is

removed

and

the

multiwalled carbon nanotubes are collected.

MWCNT

can also

be

formed

by

pyrolysis.

Quartztube

Furnace

Bubbler

&

[Thermocouple

I

CA

[image:19.484.144.341.278.421.2]

t

Figure 2.

Apparatus

for

thepreparation of

MWCNT

by

pyrolysis 12

This

apparatus shown

in Figure 2

consists of a quartztube with an

inner

diameter

of

20

mmand a

heating

zone of

200

mm

[12].

Acetylene

is

passed

through

a

liquid

Fe(CO)s

bubbler

at

300

seem

using

argon as a carrier gas

flowing

at

30

seem

[12].

The

gases and

the

catalyst are then

introduced into

the

quartz

tube

and

heated

at

750-950

C for

30

minutes

[12].

The

furnace

is

then cooled

to

room

temperature

atan

Ar

flow

rate of

500

seem

[12].

The

nanotubes are

then

collected.

SWCNT

can also

be

produced

by

the

arc

This

metal can

be in

the

form

of

Co, Co/Ni,

Co/Y, Co/Fe, Ni/Y,

Ni/Fe

with

Ni/Y giving

the

best

results.

These

catalysts promote

the

growthof

the

singlewalled structures.

The

most common methodof

preparing SWNTs is

by

laser

ablation.

Figure 3

shows

the

laser

ablation

apparatus,

which consists of a

60

cm

long

quartztubewith an outer

diameter

of

3.6

cmand an

inner diameter

of

2.7

cm

[12].

A

target

(~5um

in

diameter)

consisting

of a

compressed

graphite, Ni

and

Co

powder

is

placed

inside

the

quartz

tube

at atemperature

of

1200

C

[12].

Argon

gas

is introduced into

thequartztubeat a rate of

0.2

L/min

and a

pressure of

700 Torr.

A Nd:Y

pulsed

laser beam

is

then shown onto

the

target and

bombards

the

target surfacewith

150

pulses of

light

[12].

The laser

has

awavelength of

532

nm with a pulsewidth of

6-7

ns and a

frequency

of

10

Hz

[12]. The beam

current

is

2 J/xm

with a

diameter

of

2

mm

[12].

Once

the

laser

ablates the

target,

the nanotubes

are collected on awater-cooledcopper collector.

hjmaceat

1,200' Celsius

\

water-cooled

^^^ copper co&edor all _/ "

\

1

argon gas

m#>-:

*S^^^" ~Tfi_^A^^*..

V

' '""zniHcT{^sS***^ft P|P

\

\ narwtube leH" growing

etongfipof collector

grapfaletarget

neodymkjm-vflnunv

sJuminum-gamellaser

Fig. h.\. Singl'--wallednanotu!**>procuced in a quartz luhr-hcai.-d"

U, 1200'C hj the as^r vapor12 ation method, using a

fcraphit.*-larjl<Mandarooli-dcollectorfornanoubcs[95].

Figure 3. Laser

ablation apparatus

for

the

preparation of

SWNTs

12

an

iron

oxide catalyst

is

prepared.

Methane

is

decomposed

in

a

furnace

at

1000

C in

the

presence of

the

iron

oxide catalyst

[12].

The

iron

oxide catalyst

is

prepared

by

impregnating

alumina nanoparticles

in

methanol with

Fe(N03)2-9H20

at room

temperature

for 1 hr [12]. The

solvent

is

then evaporatedat

80C

andthe catalyst

is

then

heated

and ground

into

a powder.

The

alumina/iron oxide catalyst

is

then placed

in

a

quartztube and

heated

at

1000

C

with an

Ar flow [12]. Methane

is

then

introduced into

the

quartz

tube

at a

flow

rate of

6150

cm3/min at

1.25

atm pressure

[12].

After

lOmin,

the methane

is

thenpurged

be

reintroducing Ar [12]. The CVD

process

has

been

studied

to provide the optimum conditions

for

CNT

growth.

Other

carrier gas/catalyst

combinations

have been

used

including

n-hexane/ferrocene

thiocene

used at

RPI

[13].

1. 1. 5 Structural

Representations

Single-_{walled and multi-walled carbonnanotubes are shown}

in Figures 4

and

5.

Single-walled nanotubes consist of carbon atoms arranged

in

a

hexagon

and rolled

into

atube.

The

multiwalled carbon nanotube

in Figure 4

consists

basically

of concentric

single-walled nanotubes.

R

i^t i^^i^^ i^%i^i i^i i^Qii^^i iS

[image:22.484.191.295.33.201.2]

Figure 5.

Multi-walled carbonnanotube.15

If

the

nanotube

in

Figure 5

was opened and

laid

on a

flat

surface,

it

would

look like

Figure 6 (a

and

b),

a

flat

graphene sheet.

Figure 6

(b)

shows

how

the

helicity

of acarbon

nanotube

is

determined.

(ah.

(b)

-^. . , , A

_' .}

M a a. ,jfc _a

> a m a a >^c-50

"/'

^ * a 5 . l7i-.q:

:

! I J IS .17! SO

'

15 1 ?2ik7 ->k> f:metal '^enucorxJuctor

Figure

6.

Helicity

ofacarbon [image:22.484.132.359.342.634.2]

The

helicity

is defined

by

the

m and n

indices in

parentheseson

the

diagram

(n,m)

[11].

When

m and n are

equal, the

nanotubes are said

to

be

in

armchair

[11]

configuration.

When

m

is

equal to

zero,

thenanotubes areconsideredto

be

zigzag [1 1].

If

n and m are

different from

each other and m

is

not equal

to zero,

the nanotubesare chiral

[11].

All

armchairnanotubes are metallic as shownonthe

diagram

and

zigzag

tubes can either

be

[image:23.484.93.392.252.550.2]

metals or semiconductors

[11].

Figure 7.

Helicity

ofcarbonnanotubes.n

Figure 7

shows nanotubesof

different

helicities:

(a)

represents an armchair

nanotube,

(b)

zigzag

tubes

are

perfectly

symmetrical throughout the nanotubewhereas chiral

tubes

are

not as can

be

seen

in Figure 7 [1 1].

When

nanotubes are

formed,

they

have

endcaps on

both

ends of

the tube.

Once

they

are

purified,

the

endcaps are

broken

off as

is

shown

in

Figure 7. This

concept will

be discussed in

more

detail

in

an

upcoming

section.

1.2

Electrical Properties

Carbon

nanotubes can act either as metallic or

semiconducting

tubes

depending

on their geometry.

For

typical metallic

systems,

electrons can move

from

one metal

to

the next quite easily.

In

the case of

CNT; however,

because

they

possess such

different

electrical

properties,

electrical current will not always

flow easily from

one

tube to

the

next

[3].

Introducing

a

Schottky

barrier

into

the nanotube

(bending

the

nanotube at one

point),

allows

the

flow

of electrical current

to

continue

[3].

Nanotubes

possess

these

defects

when

they

are made and

they

can also

be

formed

by inducing

a rotation of

bonds

between

two

hexagons

to

form

a

five-fold

ring

and anadjacent seven-fold

ring

[3].

This

allows a single nanotube

to

possess

both semiconducting

and semi-metallic character

[3].

1.3 Mechanical Properties

Carbon

nanotubes

have

excellent mechanical properties

due

to

their

low

density

of

defects [16].

The Young's

modulus of

CNTs (reported

previously)

is higher

than

tubes

composed of otheratoms

[16]. This

value

only slightly

depends

on

the

diameter

of

the

nanotubes and

depends

on the

degree

of

sp2

hybridization

[16].

The Young's

modulus

is

highest

for

a

flat

graphene sheet

due

to the

fact

that

folding

the

sheet

into

a

nanotube would

distort

sp2

ratio

(v)

of a nanotube also

depends

on

its

diameter,

but

is

dependent

on

chirality

aswell

[16].

Planar

graphite

has

a

Poisson

ratio of v=

0.

17,

armchairtubes

have

a v=

0.

14,

and

other chiralities range

from

v=

0.18-0.19

[16].

When

stress

is

applied

to nanotubes,

both

thin and thick-walled nanotubes exhibit compressive strengths one order ofmagnitude

higher

than

any known

fiber [16].

Zigzag

and armchairnanotubes arethe stiffest at

0

K

[16].

Nanotubes

are also

very

flexible [16].

When

subjected

to

large

amounts of

deformation,

the nanotubes switch

into different

shapes

releasing

energy [16].

This

can

be

reversed and

is

caused

by

the

ability

of

sp2

hybridized C-C

bonds

to

reversibly

change

hybridization,

to sp3

in

this

case,

when

deformed

out ofa plane

[16].

1.4

Purification

and

Functionalization

of

Carbon Nanotubes.

There

are

many

different

methods

for purifying

and

functionalizing

CNTs.

No

matter what method

is

used to produce

MWNT

or

SWNT,

the soot

is

not

100%

nanotubes.

As

a matter of

fact,

the

purity

ofthe sample can

be

between 10-90%.

The

CNTs in

the sample come

in

three

different forms.

They

can either

be completely

closed

tubes,

have

oneend open or

have both

ends open.

The

purposeof

purifying

the

CNTs is

toremovemost orall ofthe excessamorphous graphite material and

to

open

both

ends of

all of

the

nanotubes

that

arepresent.

This

is

usually

done

in

the

presence of a

strong

acid

for

approximately

12

hrs.

The

acids

involved

can

be

hydrochloric,

nitric and sulfuric

acid.

In

most of

these cases,

the ends are opened

by

oxidating

the

carbons

in

the

pentagon

rings

of the endcaps as

they

can

be

easily

oxidized

due

to

their geometry.

When

this occurs,

carbonyl groupscan

be

found

at

the

dangling

carbon

bonds

left

on

the

[17].

thrraoooupk

team

Intolute

<

lt

/heitar 1

TtnrMWNTi wtrrhite

r

(4K)

Figure

8.

Apparatus for

the

thermal

annealing

of

CNTs.17

The

apparatus

in Figure 8

represents onethat

is

usedto

purify

thenanotubes

by

thermal

annealing.

The

cathode

deposit is

placed

in

the

inner

tube of the

furnace

and

is

constantly

rotated at

30

rpm.

The

temperature

is fixed

at

760

C

throughout.

In

this

case,

most ofthe carbonaceous material was removed and theweight was reduced

to

40%

of

the original

[17].

Purification

of

MWNT

by

intercalation

of

CuCh

[18]

has

also

been

reported.

Nanotubes

can also

be

purified and oxidized

using

ozone

[19].

In

gas-phase

ozone

oxidation,

CNTs

are placed

into

a vertical reactor

containing

a mixture of ozone

and oxygengasesand

heated

at

150-200

C

for 30-90

min

[19]. Liquid

phase oxidations

performed

by

suspending

the

CNTs in

an acidic solution

(CIO4",

Mn04*

or

H2O2)

along

with the oxygen/ozone gas mixture and

heated

at

60-70

C

for 24 hrs [19].

In

both

of

these cases,

the

endcaps,

and

any

kinks

or steps that

may

occur

in

the nanotubes

themselves,

arethe

first

to

be

oxidized andthe

bonds broken. Other

purification methods

w aler

IN

S=3

Figure 9. Irradiation

apparatus

for

purifying

nanotubes.20

Figure 9

showsthe apparatus

for

this

type

of purification.

The

cathode

deposit

from

the

carbon arc method

is

placed

directly

in

the path of

the

infrared beam.

Here,

it is

irradiated

for 30

min at

500

C

in

air.

The

productwasa

spongy

square of

MWNTs

with

a surface area of

10

mm2

and

0. 1

mmthickness

[20].

1.4.1 Chemical Properties

The

chemical properties of carbon nanotubes are now

being

extensively

explored.

Only

oneendof acarbonnanotube

is

openas

it

exists after

it is

made.

The

other end can

be

opened, exposing

the

nanotube to the

possibility

of

filling

it

with molecules

thereby

acting

as a vessel.

They

also

have

a

high

specific area which suggests

that

many

molecules can

be

adsorbed ontothe surface of

the

tubes.

As

the

nanotubes are

opened,

they

can also

be

functionalized

-other molecules can

be introduced

to the

ends of

the

carbon chains.

Carbon

nanotubes can also act as

electrodes,

increasing

the

rate of

1.4.2

Applications

The

potential applications are numerous

based

on

the

extraordinary

electrical and

mechanical properties

that

carbon nanotubes possess.

Some

recent advances and

important

research areas are

discussed

here.

It

has been

noted

that

CNTs have

the

ability

to

conductwater

by

capillary

action,

thesame

way

that

kidneys

and other small

blood

vessels movewater

[22]. There

aretwo

major

implications

here.

First,

nanotubes would

be

extremely

valuable

in

biological

systems.

This

provides

the

potential

for

artificial

organs,

such as

kidneys,

and

recently,

scientists

have

been

determining

whether

CNTs

can

be

used as artificial muscles

[23].

This

also

implies

that

CNTs

can act as carrier vessels or

"nano

test

tubes"

Small

molecules

in

solution can enter

into

the

CNTs,

as

has already been

shown

by

de

Heer,

et

al.

CNTs

were

filled

with gaseous or solution-phase metals which were

decomposed

to

solid metals

inside

the

CNTs

[24].

CNTs

can also

be

used

in

transistors

and

diodes.

They

are

very

small and

the

electronic properties are perfect

for

these types of

devices

because

electrons can move

freely

within them with

little

or no scattering.

IBM

has

drain

electrode source

electrode

' _(SO

.

^

WaWr^

i

t

fe

F

^^L^g,e

^

Figure 10.

Carbon

nanotubetransistor

from

IBM

10

They

canalso

be

used as

field

emitters

for flat-panel

displays.

Many

scientists,

recently,

have

been

testing

nanotube/polymer composites.

Nanotubes

have

superior mechanical

properties compared

to polymers,

so

the

addition of

CNTs

should provide

increased

strength and

hardness.

They

have

also

been

added

to

conducting

polymers

to

increase

the

electrical properties ofthepolymers.

In

the

US,

we are always

looking

for

ways to

increase

energy efficiency

and

to

eliminate pollution.

Recently,

the

president

has

granted a

bill

that provides

money for

hydrogen

fuel

cell research.

CNTs

play

a

big

role

in

this

category.

They

have been

shown

to

be

highly

efficient

for

the

storage of

hydrogen

gas.

A

single gram of carbon

nanotubes can absorb

>3

wt%

hydrogen

under

290 K

and -10

MPa

[25]

which

is

potentially

useful

for

fuel

cell applications.

Purified MWNTs

have

also

been

used

to

electromechanically

catalyzeoxygen reduction

in fuel

cells.

Batteries

can

be

made

using

CNTs

that

will

have

an

improved

lifetime

overtraditionalmetal catalyzed

batteries

[26].

gases or

for

chemical analysis.

Conducting

polymer/CNT composites

have

already been

used

in

_{gas-detection sensors.}

The

hope is

that

_{we will}

be

able

to

use

CNTs

in

a

very

small apparatus

that

could

be

remotely

operated

to

areas where

humans may

be in

harm.

These

small sensors could

easily be

undetected and couldtransmit

information regarding

the

purity

of

the

air or water.

CNTs

can also

be

used

in

microscopy.

Recently,

atomic

force

microscopes

have

been developed

that

use a carbon nanotube as a

tip

ratherthana gold electrode

[27].

We

are

moving

toward smaller

dimensional

particles and we need

to

be

able to analyze

surfaces

in

the

smallest

dimensions.

Using

a single carbon nanotube at

the

tip

ofan

AFM

allows us

to

analyze surfaces on the order of

nanometers,

which

has

never

been

done

before. Thus

the

foundation

for

the

development

of nanoscience

has

emerged.

1.5

Nanoscience

Nanoscience

is

most

widely defined

as

the

phenomenon associatedwithstructures

roughly in

the

1-100

nm range wherethe properties are of

interest due

to

the sizeofthe

structure,

and are

typically

different

than those of a molecule or a comparable

bulk

material.

We

plan

to

prove that whena reaction

is

confined to nanodimensional carbon

structure, the

products are

different

than

in

the

bulk

solution.

Basically,

any

chemical

object ofsubmicrometer

dimensions

orwith submicrometer

features

can

be

considered a

part ofnanoscience.

Why

is

nanoscience

important? When

matter

is

confined

to

a small

space,

as will

be

proven

in

this

thesis,

phase transitions can occur

that

cannot

be

observed

in larger

This

will allow us

to

get

information faster

than

ever.

Resist layers may

be

deposited

monomolecularly

which will allow

for

the

smallest

devices

possible.

Research

in

nanoscience

has

allowed

for

the

development

of

conducting

polymers as thin

film

transistors.

Chemical

applications

in

nanoscience

include

building

molecules

from

the

bottom

up.

We

may be

able

to

build

a molecule piece

by

piece with specific stereochemistry.

The

possibility

of

developing

monodisperse assemblies of clusters

to

form

high

molecular weight units

has

also

been

realized.

1. 5. 1

Nanodimensional

Reactions

A

nanodimensional reaction

is defined

as a reactionthatoccurs

in

a spacewhere

at

least

one

dimension

is less

than

1

um.

When

a reaction

is

confined

to

a

very

small

space, the

molecules are

forced

to

reactwitheach other where

they

wouldnot

ordinarily

do

so.

This

allows

for different

products

in

the nanoscale thanwould

be formed

in

the

macroscale.

In

this case,

areaction

is

confinedwithin a carbon nanotube.

10-50

nm

Figure

11.

Reaction

inside

acarbonnanotube.

solution and

diffuse into

the

carbon nanotube through two

forces.

First,

the

solution

is

being

pulled

into

the tube

by

capillary

action.

Secondly,

the

light-colored

spots

located

on

the

inside

ofthe

CNTs

represent electron

densities

on

the

nanotube.

Electron

densities

are present anywhere on

the

nanotube where a

kink

or

step

is

found,

or where

the

nanotube

bends for

any

reason.

They

are chargesthat

build

up

onthe

surface or within

the

nanotube that occur

during

the synthesis ofthe nanotubes.

These

electron

densities

are

negatively

charged and

they

help

to attract the

partially

positive

charges on

the

molecules and

hold

themuntil

they

can reactwithother molecules present.

Hertel,

et al. showed

that

carbon nanotubes can

be

manipulated

by

an

AFM

tip,

that

is,

they

can

be bent

at

the

point wheretheelectron

densities

occur

in

thenanotubes

[28].

1.6

Purpose

of

the

Thesis

The

purpose of

this thesis

is

threefold.

The

first is

to examine

the

catalytic nature

ofthe multiwalled carbon nanotubes

in

organic oxidative reactions where

the reactants,

intermediates

and products are present

in

the confined tubular

topology

of carbon

nanotubes

containing

flexible

electron

densities.

For

this

purpose,

the

chemical

oxidationsof

primary

and

secondary,

aromatic and

aliphatic,

amines

have

been

chosen as

they

form

an

important

class

for producing conducting

polymers through a colored

intermediate

species.

The monitoring

of

any

chemical reaction within

the

nanotube

directly

is

an uphill task except

in

situations where

the

product

is deposited

as a solid

metal and can

be

analyzed

by

Transmission

Electron

Microscopy

[24].

As

it is

impossible

to

determine

whether reactants are situated

inside

a

nanotube,

there

has

not

nanotubes.

If

a reaction produces a colored product

inside

the

carbon

nanotube,

then

its

diffusion into

the

outer solution could

be

monitored

by

optical absorption spectroscopy.

As

this

is

generally

a slow

process,

a

time

dependent

absorptionprofile

is

to

be

expected

in

the

above oxidative reactions.

The

second aspect of

this

study

is

to examine the synthetic schemes

in

the

oxidation of

amines,

suchas aniline

and/?-toluidine,

when carbon nanotubesare present.

The

third

aspect

is

to

study

the

effect of a column configuration of carbon

nanotubes on

the

product yield

in

the

above

oxidations, and,

to compare

its

performance

to carbon nanotubes suspended

in

the medium.

When

thecarbon nanotubes are arranged

in

a column

configuration,

the

reactants are

continuously

in

contact with

the

carbon

nanotubes.

This

reducesthe

interference

arising from

theoxidative reactions

occurring in

thesuspended medium.

The

multiwalled nanotubes used

in

theoxidationoftheabove amines are purified

and

functionalized using

a modified method of

Green,

et al.

[29].

They

are analyzed and

characterized

by

FTIR,

SEM

TEM

and

TGA.

The

products obtained

in

theoxidation of

amines are

analyzed,

characterized and

determined

by

UV-VIS, GC/MS,

Fluorescence

and

FTIR.

Based

on the analytical

data,

the reaction and

kinetic

mechanisms are

determined.

The

results pointto the

feasibility

of

constructing

a carbon nanotube-based

2.

Experimental

2.1

Chemicals

/?-Toluidine and methylamine

(41% in

water)

were purchased

from

Aldrich

and

used as received.

Aniline

(Aldrich)

was purified

by

distillation.

The

sample was

collected at

1

80C,

sealed and

kept

underrefrigerationuntil

further

use.

Azobenzene

was

purchased solid

from

Aldrich

and

kept

in

a

dessicator

until use.

Hydrogen

peroxide

(30%

vol/vol) (Baker Analytical grade)

was

kept

under refrigeration and used

in

all ofthe

experiments.

All

solvents were

Baker Reagent

or

Analytical

grade and used asreceived.

Nitric

acid

(69.0-70%)

(Baker Analyzed ACS

Reagent)

was used

in

the

functionalization

of

the

nanotubes.

Fisher

Scientific

Decolorizing

carbon

(Norite)

was used as the active

carbon sample.

2.2 Instrumentation

2.2.1

UV-VIS Analysis of

the

Reaction

All

reactions were monitored

using

a

Shimadzu UV2000

series spectrometer.

The

method parameters

for

the

instrument

were as

follows:

wavelength=

200-800

nm

scan,

slit width =

0.5

mm,

scan speed =

medium.

A

quartz cuvette was used

for

all

experiments.

All

experiments were performed

using

thesolvent asthe

blank.

2.2.2

GC/MS

Characterization of

the

Products

with

HP 5973

mass selective

detector

and

fitted

with an

Agilent (19091

S-396)

column).

The

GC

column used prior to

January

2002

was an HP-

IMS

(100%

dimethylpolysiloxane)

which

had capillary

measurements of

60

m x

250

um x

0.25

urn

nominal.

The

column used after

January

2002

was an

HP SPB-5 (5%

Phenyl,

95%

Polysiloxane)

which

had capillary

measurements of

15.0

mx

200

pmx

0.20

umnominal.

A

standard method was used with

this

column when

determining

the

formation

of

different

azo groups.

The

injection

temperature

was set at

280

C

and

helium

gas

flowed

at a rate of

1

mL/min with

the

flow

rate ofthe column set at

2.2

mL/min.

The

column

temperature

was set at

80 C for

1 minute,

then

increased

to

220

C

at a rate of

20

C/min

and then

increased

to

280 C

at a rate of

4

C/min.

The

injection

ofthe sample ranged

from

1

to

5

uL.

2.2.3 FTIR of

Carbon

Nanotubes

andthe

Products

Infrared

spectrawere

determined using

a

Bio-Rad FTIR

spectrometer

(Excalibur

Series).

Solid

samples were analyzed

using

a

diffuse

reflectance attachment.

Multiwalled

carbon nanotubes were ground

in KBr

and

kept

in

the

powder

form

during

analysis.

Liquid

samples wereplaced

between

two

KBr

salt plates and placed

directly

in

thepathofthe

infrared beam.

2.2.4 TGA

of

Carbon Nanotubes

The

carbon nanotube samples were analyzed

for

their

thermal

degradation

temperatures

using

a

Universal TA TGA Instrument (model

V2.6D).

Samples

were

2.2.5

Fluorescence Spectra

ofAzobenzene

andthe

Products

A

Perkin-Elmer

Luminescence

Spectrometer LS50B

was used to

determine

the

fluorescent

properties of

azobenzene, aniline,

acetonitrile andacetone.

2.2.6 Atomic Absorption of

Carbon

Nanotubes

The

carbon nanotubes were sonicated

in

a nitric acid solution and analyzed

for

Cu

and

Fe

content

using

a

Perkin-Elmer AAnalyst

100

atomic absorption spectrometer.

2.2.

7pH of

the

Carbon

Nanotubes

The

carbon nanotubes were sonicated

in

water and analyzed

using

a

VWE

pH

meter

Model

#8005

with

Accumet

glassand reference electrodes.

2.3 Procedures

2.3.1 Functionalization of Carbon Nanotubes

Multiwalled

carbon nanotube core material was purchased

from

DEAL

International,

Nanotechnology

Division.

To

functionalize,

open and

purify

the carbon

nanotubes,

2 g

carbon nanotube core material were suspended

in

43

mL concentrated

nitric acid and refluxed

for

12-24

hrs.

at atemperature of

140

C.

The

nanotubes were

thenwashed several timeswith

distilled

water and thenrefluxed

in

distilled

waterat

100

C for

approximately 5-10 hrs.

The

nanotubeswerethen

filtered

and

dried

overnight

in

a

Polytechnic Institute

and

functionalized in

the

above manner.

2.4

Oxidation

of

Aniline.

Aniline

and

hydrogen

peroxide were reacted together

in

acetonitrile,

acetone,

hexane

or methanol

in

the

presence of

functionalized

CNT,

nonfunctionalized

CNT,

activated charcoal and graphite

in

a

honeycomb

sheet received

from

Prof. D. D. L.

Chung

at

the

University

of

Buffalo.

The

reactions were performed at room temperature and at

40

C for

comparison.

Various

amounts of

CNT

were addedto

the

solution

for kinetic

studies.

Upon

formation

ofthe simulated

nanomachine,

a solution of

aniline,

hydrogen

peroxide and solvent was mixed and added

dropwise

to

the

CNT

column.

The

products

wereanalyzed

by

GC/MS

and

UV-VIS

in

all cases and

by

Fluorescence spectroscopy in

some.

2.5 Oxidation

of/J-Toluidine.

/?-Toluidine and

hydrogen

peroxide were reacted together

in

acetone or

acetonitrile

in

the presence of

functionalized

carbon nanotubes and

varying

amounts of

nonfunctionalized

CNT.

A

control solution was made

that

contained

only

the

two

reactantsand solvent

for

comparison.

All

reactions were performed at room

temperature

unless otherwise noted.

Upon

completion of

the

simulated

nanomachine, the

solution

was prepared and then

introduced

into

the

CNT

column

dropwise.

The

products

in

all

2.6

Oxidation

of

Methylamine.

A

1:1

ratio of methylamine

to

hydrogen

peroxide solution was prepared

in

acetone and acetonitrile

in

the

presence of

functionalized

CNT.

A

control solution was

also made

for

comparison

that

contained no

CNT.

Upon

preparation of

the

simulated

nanomachine,

the

solution was prepared

in

a

test tube

and then

introduced into

the

CNT

column

dropwise.

The

products

in both

cases were analyzed

by

GC/MS

and

UV-VIS.

2.7

Oxidation

of

Diphenylamine.

A

1:1

solution of

diphenylamine

to

hydrogen

peroxide

in

acetonitrile was

prepared.

This

solutionwasthen added

dropwise

to

the

functionalized

CNT

column and

the

product obtained was analyzed

by

GC/MS

and

UV-VIS

spectroscopy.

3. Results

and

Discussion

3.1 Characterization

of

Carbon Nanotubes.

3.1.1

Fourier Transform

Spectroscopic Studies

Multiwalled

carbon nanotubeswere analyzed

using

the

FTIR

spectrometer

before

and after

functionalization

to

determine

whether there

is

a change

in functional

groups

during

the

process.

Figure

12

shows the

IR

spectrum

before

the

tubes

were

47"

impurecnt.bsp(2)

46

5-<D O

C

oq 46

0-c C

45

5-45

0-44

5-J{

44

0-t ,i,l.,,,l,, r 1 t i i i i i i i . i . . ti iiit i > i i i 1400

2800 2600 2400 2200 2000 1800 1600

Wavenumber

Figure 12.

FTIR

spectrum of carbon nanotubes prior

to

functionalization.

It

can

be

noted

that

no carbonyl peak

(1600-1800

cm"1)

can

be

observed

in

this

spectrum.

The

peaks are rather weak

in

this

spectrum

due

to the

reflection of

the

light

scattering

off

of

the

nanotubes.

However,

when

comparing

this

spectrum with

the

Figure

13,

there is

a

significantpeak

difference

after

functionalization.

Figure 13. FTIR

spectrumof carbon nanotubes after

functionalization.

A

peak

is

presentat

1880

cm"1

after

functionalizing

the

carbon nanotubes which

indicates

nanotubes,

but

it

oxidizes some of

the

end groups and

defect

centers

to

carbonylgroups.

3.1.2

Thermogravimetric Studies

The

nanotubes

before

and after

functionalized

were analyzed

by

thermogravimetric

analysis

to

determine

whether

the

degradation

temperature

and

characteristics change

during

functionalization.

Figure 14

shows

the

TGA

graph of

the

core ground material as received.

The

material

begins

to

degrade in

the range of

560

to

720 C.

100%

ofthe

starting

material

(3.865 g

core

material)

was

degraded

under air

flow.

Sample: Unpurified CNT Size: 3.3550_mg Method:Ramp

Commentatmosphere-air

TGA

File:unpurrfiedcarbon nanolu...

Operatorrajrv

RunDate:9-Apr-02 i 1:06

,-I

100J

80-\

\

\

\

\

20-\

\

\

0-

V

^

(J 200 400 60C BOO 1CK

Temperature

(CC)

UnwersalVZ.6D TA Instruniente

Figure 14. TGA

graphof

CNT

prior

to

functionalization.

shows a phase

transition

at

approximately

the

same

temperature,

580

C,

but does

not

finish

degrading

until almost

900

C,

a

difference

of almost

200

C.

There

is

no residue

left in

this

experiment.

This

difference

could

be due

to the

carbonyl end groupsthat

have

been

acquired

during

functionalization.

It

would

be harder

to

oxidize

the

carbonylgroups

than

to

oxidize pure

carbon, causing

the

breakdown

of

the

carbon nanotubes

to

take a

longer time,

providing

a

longer

range of

degradation in

the

TGA data.

The

spectra

clearly

show a

difference between

the

two samples of

CNT.

Sample:pimSed earner nanotubes trar

Size: B.2390mg

Method: ftamc

TGA

File-_{C:_vunT*a}

crt n ar Operatorrapv

Rut. Dale: 7-Apr-0220:18

120- -oo-

60-\

\

\

a 3

\

\

\

\

40-\

i

Z>-\

\

\

D 20G 400 00

Temperature(=0)

?:: i

UrncnslVSGD

WO

TAntum-,1

Figure 15. TGA

spectrumof

CNT

after

functionalization.

3.1.3

Scanning

Electron Microscopic Results

The

carbon nanotubes were taken

to

RPI

(Troy, NY)

to

be

analyzed

by

SEM

and

determine

what

the

content ofthematerial was.

Figure 16

shows

the

SEM

image

of

the

carbonnanotubes after

functionalization.

The

image

shows

mostly large

masses of

gray

nanotubes.

This

analysis shows

that the

carbon nanotube

bundles

were present after

purification.

The

samples

from

RPI

were

relatively

non-bundled and showed separated

tubes.

Figure 16. SEM image

of

functionalized

carbon nanotubes.

3.1.4 Transmission Electron Microscopic Studies

The

carbon nanotubes were then analyzed under a

transmission

electron

microscope also at

RPI

to

determine

the characteristics of

the nanotubes,

i.e.,

whether

they

were

opened,

whether

defect

centers were

present,

and what changes

may

have

[image:43.484.117.371.274.476.2]

Figure 17. TEM

analysis of closedcarbon nanotube.

Figure 18. TEM

analysis ofa

functionalized

carbon nanotube.

Comparing

Figures 17

and

18

provides

important information regarding

the

change of

the

CNTs

after

functionalization.

Before

functionalization,

the

nanotubes

have

a closed

end,

the

pointed end of

the

nanotube

in Figure 17.

In

both

figures,

the

hollow

center of

the

nanotube can

be

seen and

the

many

layers

of

the

multiwallednanotube are visible.

After

off.

The

nanotubes

have

also

been broken

in

some places

by

the

nitric acid.

3.2

pHof

Carbon Nanotubes

To

ensure

that

there

was no nitric acid

left

on

the

nanotubes,

60

mg

of

functionalized

CNT

were placed

in distilled

water and sonicated

for

1

hr before

being

analyzed

for

the

pH of

the

water.

It

is

assumed that after

1

hour

of

sonication,

any

nitric

acid

that

may

be

adsorbed onto

the

surface or

may

have diffused into

the

nanotubeswill

be

removedand

left in

the

watersolution.

Table 1

givesthevalues

from

this

experiment.

It

is

obvious

from

these

results that

there

is

no nitric acid

left

afterthe

washing

process

from functionalization

ofthe tubes.

The

overall result

is

asolution that

is

slightly

more

basic

than

distilled

water.

*

Table

1.pHofFunctionalized Carbon Nanotubes

pH ofbuffer ,,. .... . pHof

CNTs

v

, . pH ofdistilled . , solution v , sonicated in

water

(7.00)

water

1 7.03 7.14 7.51

2 7.03 7.18 7.59

3 7.02 7.15 7.63

4 7.03 7.13 7.57

5 7.03 7.14 7.56

average 7.028 7.148 7.572

Std.

Dev. 4.47E-03 1.92E-02 4.38E-02

3.3 Atomic

Absorption

of

Functionalized

Carbon Nanotubes

3.4

Oxidation

of

Primary

Amines

3.4.1

Aniline-Discovery

of

the

Effect

of Carbon Nanotubes

The

initial

experiments were performed with

1 M

aniline and

1

M hydrogen

peroxide

in

25

mL of acetonitrile

(control

solution)

in

a reflux at

60

C for

3

hours.

After

the

first

hour,

the

solution

began

to

turna

light

yellow color and after

the second,

a

darker

yellow color.

At

this

point,

no carbon nanotubes

had been

added.

The

solution was

analyzed

by

GC/MS

and

the

major peaks seemed to

be

aniline,

acetonitrile and carbon

dioxide

although nitrobenzene and nitrosobenzene were also

formed

after

24

hours.

Carbon

nanotubes werethenadded

to

a

different

1

M

aniline and

1

M

hydrogen

peroxide

solution and refluxed

for

3

hours

at

60

C. At

the

end of

the three

hours,

the

solutionwas

a

deep

red

in

color

(see Figure 19).

Due

to

the

color of

the

solution with carbon

nanotubes,

it

was

decided

that

UV-VIS spectroscopy

should

be

performed.

The

control

solution wasthen analyzed.

The

peaksweresaturated

in

the

range of

190-3

10

nmand no

otherabsorptionpeaks were observed.

The

peaks

in

thisrangeare

due

to

theacetonitrile

and aniline and are apparent

in

all

UV-VIS

spectrathat contain aniline and acetonitrile.

The

solutionwith

CNT

alsocontainedthesepeaks

along

with apeak

in

the

347

nm

range,

a peak

in

the

440

nm range and a peak

in

the

510

nm range.

The

solutions were

very

.

ttl'

tic

fi Br'"'

i ^^^w

Control

Funct

Nanotubes

CNT

as

Received

Figure 19. Photograph

ofreaction

in

cuvettes.

3.4.2 Influence ofHydrogen Peroxide Concentration

The

next

step

of experimentation

included making

solutions

that

contain

1M

aniline and

2 M

hydrogen

peroxide

in 25

mL of acetonitrile.

One

solutioncontained

100

mg CNT

and one control solution without

CNT.

These

solutions were stirred at room

temperature

for

three

hours.

The

solution without

CNT

became

a

light

yellowcolor and

the

solution with

CNT

became

a

dark

red color at the end of

the three

hours.

The

solutions were

then

analyzed

by

GC/MS

and

it

was

determined

that

aniline, acetonitrile,

carbon

dioxide,

nitrobenzeneandnitrosobenzenewerepresent

in both

samples;

however,

the

solutionwith

CNT

produced

both

more nitrobenzene and more nitrosobenzene

than

the

solutionwithout

CNT

when

comparing

peakareas.

Solutions containing 1 M

aniline

and

3 M hydrogen

peroxide were

then

made

in 25

mL

acetonitrile,

one

containing 100

mg

of

CNT

and onewithout.

The

solution without

CNT

again

turned

a

light

yellow color